High sensitivity visible infrared photoconductor

ABSTRACT

A photosensitive element which includes a photoconductive insulating layer comprising a vitreous alloy of selenium, bismuth and iodine.

United States Patent Hillegas et a1. Aug. 5, 1975 HIGH SENSITIVITY VISIBLE INFRARED 2,962,376 11/1960 Schaffert 96/1 PHOTOCONDUCTOR 3,041,166 6/1962 Bardeen 96/1 3,312,548 4/1967 Straugham 96/l.5 [75] Inventors: William J. Hillegas, Falrport; Jam s 3,460,476 8/1969 Swigert et a1. 96/1.5 H. Neyhart, Penfield, both of NY. 3,607,388 3/1967 Hori .1 252/501 [73] Assignee: Xerox Corporation, Stamford,

Conn Primary ExaminerN0rman G. Torchin 22 i J 5 1973 Assistant ExaminerJohn L. Goodrow [21] Appl. No.2 321,164

52 us. (:1. 96/l.5 [57] ABSTRACT [51] Int. Cl G03g 5/00 [58] Field 61 Search 96/1 .5; 252/501; 313/94, A h q f element a photocon' ductwe msulatmg layer compnsmg a v1treous alloy of 313/101, 250/316, 317, 29/572 selemum, blsmuth and 1od1ne.

[56] References Cited F UNITED STATES PATENTS l0 Clalms, 5 Drawlng lgures 2,862,815 12/1958 Sugarman, Jr. et a1. 96/1.5

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00617 0062 0062 (03s mpuom 5110A) HIGH SENSITIVITY VISIBLE INFRARED PHOTOCONDUCTOR BACKGROUND OF THE INVENTION This invention relates to xerography and more specifically to a system utilizing an improved photosensitive member and composition.

In the art of xerography it is usual to form an electrostatic latent image on a member or plate which comprises an electrically conductive backing member having a photoconductive insulating surface thereon. One example of such a member comprises a layer of vitreous selenium contained on a conductive substrate. This imaging member is characterized by being capable of receiving satisfactory electrostatic charge and selectively dissipating the charge when exposed to a light pattern, and in general is largely sensitive to light in the blue-green spectral range. The electrostatic charge pattern formed by the selective dissipation of charge may be converted into a visible image by developing with electroscopic material called toner.

The use of vitreous selenium in xerography has had wide acceptance because of its capability of holding an electrostatic charge for long periods of time when not exposed to light, and because of its relative sensitivity to light when compared to other photoconductive materials. In addition, vitreous selenium has sufficient strength and stability to be reused hundreds or even thousands of times.

In order to improve the resistance of vitreous sele-- nium to crystallization, and to enhance light sensitivity and response to longer wavelengths, elemental arsenic in varying concentrations is added to the selenium. One significant contribution with respect to the addition of arsenic is taught by US. Pat. No. 2,803,542. Notwithstanding the use of selenium, and improvements such as arsenic additions, there is a continuing need for xerographic photoconductors which exhibit a panchromatic response and higher sensitivities to various wavelengths.

It is therefore an object of this invention to provide an improved photosensitive member suitable for use in xerography.

It is another object of this invention to provide a selenium-bismuth-iodine photoconductive composition having a broadened range of spectral response.

SUMMARY OF THE INVENTION The foregoing objects and others are accomplished in accordance with this invention by providing a novel photosensitive vitreous or amorphous ternary alloy comprising selenium, bismuth and iodine. The novel alloy of the instant invention has been found to exhibit a panchromatic response which is significantly higher than that of other photoconductors such as selenium or selenium containing arsenic in amounts up to about 40 atomic percent. The higher sensitivity of the photosensitive alloy of the present invention is especially evident for light whose wavelength is greater than about 600 nanometers (6,000 Angstrom Units).

More specifically, it has been discovered that the vitreous alloy of selenium, bismuth and iodine, in concentrations of about 90 to 97 atomic percent selenium, about 1 to atomic percent bismuth, and about 2 to 5 atomic percent iodine yields the desired advantages enumerated above. A preferred concentration of about 94 atomic percent selenium, about 3 atomic percent bismuth, and about 3 atomic percent iodine exhibits maximum sensitivity. Percentages of bismuth and iodine falling below the above ranges exhibit a low red response, while compositions falling above the concentration range for bismuth and iodine exhibit a high dark discharge. In addition, higher concentrations of bismuth and iodine tend to lead to crystallization of the alloy layer, making it unsuitable for use in xerography.

The advantages of the improved photosensitive alloy of the instant invention will be apparent upon consideration of the following disclosure of the invention and especially when taken in conjunction with the accompanying drawings wherein:

FIGS. 1a, lb, 1c and 1d illustrate various structural embodiments which may employ the alloy composition of the present invention.

FIG. 2 graphically illustrates the sensitivity of various alloy compositions of the present invention compared to two photoconductive materials of the prior art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The selenium-bismuth-iodine alloys of the present invention may be prepared by any suitable technique. Typical techniques include vacuum evaporation in which either coevaporation or flash evaporation methods are employed.

In coevaporation the appropriate amount of the selenium, bismuth and iodine are placed separately in heated crucibles and maintained in the vacuum chamber under suitable vacuum conditions such as from about 10' to 10' Torr. The crucibles may comprise any inert material such as quartz, metal or ceramic lined metal. The components to be evaporated are each maintained at a temperature between about their respective melting points and well below their boiling points. Evaporation is carried out for a time sufficient to form a layer of desired thickness. In general, a film thickness of about 10 to 40 microns is obtained where evaporation is continued for a time ranging from about 1 to 3 hours at a vacuum of about 5 X l0" Torr. Generally during evaporation, the substrate to be coated is supported above the heated crucibles and maintained at a slightly elevated temperature in the vicinity of 50 to C. When cylindrical substrates, such as an aluminum drum is used, it is generally rotated above the evaporation source during the coating step.

When a multicomponent photoconductive composition or alloy layer is formed, a preferred method of forming the photoconductive layer comprises flash evaporation under vacuum conditions similar to those defined for co-evaporation. In this method, a master alloy of the desired composition having a partical size less than about 0.5 millimeters in diameter is selectively dropped into a heated crucible maintained at a temperature of about 600C to 800C. The vapors formed from the heated mixture are evaporated upward onto a substrate supported above the crucible. This procedure is continued until the desired thickness of the vitreous selenium-bismuth-antimony alloy has been formed on the substrate.

The alloys of this invention may be conveniently formed on any conductive or insulating substrate. The substrate may comprise a metal plate or cylinder such as brass, aluminum, platinum, stainless steel or the like. The substrate may be in any convenient thickness, rigid or flexible in the form of a sheet, web, cylinder, or the like, and may be coated with a thin layer of plastic. It may also comprise such materials such as metalized paper, a plastic sheet covered with a thin coating of aluminum or copper iodide, or glass coated with a thin layer of tin oxide or chromium. Generally, in forming most xerographie members, in order to obtain the desired electrical characteristics, a thin barrier layer is normally formed between the photoconductive layer and the substrate. This'barrier layer may comprise a thin oxide or organic coating, which is formed on the substrate before depositing the photoconductive layer. In addition to the above, in certain cases, the substrate may even be dispensed with, if desired, following the formation of the photoconductive layer.

The thickness of the selenium-bismuth-iodine alloy is not particularly critical. The layer can be as thin as about 1 micron or less, or as thick as about 300 microns or more, but for most applications, the thickness will generally be between about to 80 microns when the layer is used alone on a supporting substrate.

One embodiment of the present invention comprises using the selenium-bismuth-iodine alloy in a single layered configuration. Imaging member 10, of FIG. la illustrates this configuration in which a supporting substrate 11 contains a selenium-bismuth-iodine layer 12.

In another embodiment, an imaging member (FIG. lb) comprises a supporting substrate 21, having a relatively thick photoconductive layer 22, such as selenium or selenium-arsenic, overcoated with a relatively thin layer 23 of the selenium-bismuth-iodine photoconductive alloy of the present invention. During imaging in the xerographic mode, imaging light is absorbed in the top layer 23, and positive charges or holes are transported through the lower photoconductor layer.

In a further structural embodiment (FIG. 1c), an im' aging member 30 comprises a supporting substrate 31, a thin layer of the selenium-bismuth-iodine photoconductor 32 over the substrate, and a top layer of the electrically active material such as polyvinyl carbazole or polyvinyl pyrene. This member may be imaged with light to which the active layer is transparent and to which the photoconductor layer is absorbing. The electrical charges, which are transported through the active layer and discharge a surface charge, result in the formation of a developable latent electrostatic image. In this configuration, the thickness of the active layer is usually considerably thicker than the photoconductor layer. A preferred thickness range which gives optimum electrical characteristics comprises a range of about 10 to 20 microns for the active layer, and about 0.03 to 1 microns for the selenium-bismuth-iodine pho toconductor alloy. This concept is more fully described in copending application, Ser. No. 94,139, filed Dec. 1, 1970.

Another composite configuration contemplated by the present invention comprises an imaging member 40 (FIG. 1d) having a supporting substrate 41, with an electrically active layer 42 contained over the substrate. A thin layer of the selenium-bismuth-iodine photoconductive 43 is formed over layer 42. Alternatively, layer 42 may comprise an electrically insulating organic material. This structure is especially suitable for reflex-type imaging. A similar type of structure is more fully described in US. Pat. No. 3,573,906.

In addition to the above configurations, the photoconductive alloy of the present invention may be ground into fine particles and dispersed in any suitable binder and used as a photoconductive binder layer. The binder may be photoconductive, electrically active, or electrically insulating.

The following examples further specifically define the present invention with respect to the method of making a selenium-bismuth-iodine photoconductive layer. The percentages of the disclosure, examples, and claims are atomic percentages unless otherwise indicated. The examples below are intended to illustrate various preferred embodiments of making photoreceptors utilizing a selenium-bismuth-iodine photoconductive alloy.

EXAMPLE I A selenium-bismuth-iodine photoconductive alloy comprising 94 atomic percent selenium, 3 atomic percent bismuth, and 3 atomic percent iodine, is formed by placing the appropriate amount of each element in a quartz ampoule and sealing the ampoule. The ampoule is then placed in a vacuum environment at a vacuum of 10 Torr and heated at 600C for about 12 hours. The alloy materials comprise selenium having 99.999 percent purity, available from the American Smelting and Refining Company, South Plainfield, NJ. The bismuth comprises 99.9999 percent purity available for Cominco American, Incorporated, in Washington. The iodine has a purity of 99.99 percent, Baker Analyzed Reagent Grade, available fro the J. P. Baker Chemical Company, Phillipsburg, NJ. Following heating at 600C for 12 hours, the ampoule is quenched in water and the resultant vitreous alloy removed from the ampoule. The alloy is then crushed and sized to a particle size range of about 0.149 mm to 0.42 mm.

EXAMPLE II A 10 micron film of the vitreous-selenium-bismuthiodine alloy formed by the method of Example I, is formed on a fiat 2 inch square aluminum substrate 'containing a thin aluminum oxide surface layer. Thirty grams of the alloy is placed in a hopper within a vacuum chamber and fed at a controlled rate into a heated quartz crucible which is maintained below the hopper.

EXAMPLE III Five additional alloys are made by the techniques of Example I. These alloys are then used to make five additional plates using the method of Example 11. These plates have the following composition:

Se(At%) Bi(At%) I(At%) In addition to the above, two control plates are made, one comprising a layer of all vitreous selenium and the other comprising a vitreous selenium alloy containing arsenic in an amount of about 40 atomic percent (designated As se The spectral response of the plates made by Examples II and Ill, including the two control plates, are measured using a reciprocating flat plate scanner. The plate sample is charged in the dark as it moves under a corotron, and then stops under a wire d.c. electrometer probe. A Keithley Model 300 electrometer amplifier emits a voltage proportional to the plate surface potential and is recorded on one channel of a Sanborn Model 7712 B recorder. The same output voltage is differentiated by a Philbrick P45ALU operational amplifier and displayed on the second recorder channel. A monochrometer illuminates the sample surface through the transparent electrometer probe. This allows both dark and light discharge to be monitored continuously. If desired, the monochrometer can be replaced with another light source such as a fluorescent light. A Tungsten lamp filtered by a 380 nanometer interference filter set is used to discharge the remaining potential from the sample in preparation for the next test.

The spectral response of the six alloys of the instant invention is compared to the control plates containing the layer of selenium and a second plate containing a layer of 60 selenium 40 arsenic (As Se It can be seen from the data shown in FIG. 2, that the seleniumbismuth-iodine alloys of the instant invention exhibit a high photosensitivity for light whose wavelength is greater than about 600 nanometers. Further, the alloys of the instant invention exhibit a panchromatic response which is significantly higher than the selenium alone or the selenium-arsenic alloy.

Although specific components and proportions have been stated in the above description of the preferred embodiments of the invention, other suitable materials and procedures such as those listed above may also be used with similar results. In addition, other materials may be added which synergise, enhance or otherwise modify the properties of the photoconductive alloys of the present invention.

Other modifications and ramifications would appear to those skilled in the art upon reading the disclosure. These are also intended to be included within the scope of this invention.

What is claimed is:

1. A photosensitive element which includes a photoconductive insulating layer, said layer comprising the vitreous alloy of selenium, bismuth and iodine comprising about 1 to 5 atomic percent bismuth, 2 to 5 atomic percent iodine, with the balance substantially selenium.

2. The element of claim 1 in which the composition comprises about 3 atomic percent bismuth, about 3 atomic percent iodine and about 94 atomic percent selenium.

3. A photoreceptor member comprising an electrically conductive support member having a photoconductive insulating layer thereon, said photoconductive layer comprising a vitreous alloy of about to 97 atomic percent selenium, l to 5 atomic percent of bismuth and 2 to 5 atomic percent iodine.

4. The member of claim 3 in which the photoconductor composition comprises about 94 atomic percent selenium, 3 atomic percent bismuth and 3 atomic percent iodine.

5. A photoreceptor member which comprises:

a. a supporting member;

b. a thin layer of a vitreous selenium-bismuth-iodine photoconductive alloy overlaying said support; and

c. a layer of an electrically active organic material overlaying said photoconductive layer.

6. The member of claim 5 in which the photoconductive layer is about 0.03 to 1.0 microns in thickness.

7. The member of claim 6 in which the active layer is about 10 to 20 microns in thickness.

8. The member of claim 5 in which the active material comprises a material selected from the group consisting of polyvinyl carbazole and polyvinyl pyrene.

9. A method of imaging comprising:

a. providing a xerographic member which includes a photoconductive insulating layer having a composition comprising a vitreous alloy of selenium, bismuth and iodine in a concentration of about 1 to 5 atomic percent bismuth, 2 to 5 atomic percent iodine, with the balance substantially selenium;

b. substantially uniformly electrostatically charging said member; and

c. exposing said member to a pattern of active radiation to form a latent electrostatic image thereon.

10. The method of claim 9 which further includes developing said image to make it visible.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 31 898, 083

DATED August 15, 1975 !NV ENTOR(S) William J. Hillegas, James H. Neyhart It is certified that error appears in the ab0ve-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2 line 53, delete partical" and insert particle.

Column 4 line 27, delete "for" and insert --1Ero-m-.

Column 6, line 28, delete "microns" and insert micron.

Signed and ficalcd this twenty-eight D ay Of October I ,9 75

[S AL] A ttes t:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner uj'Parenls and Trademarks 

1. A PHOTOSENSITIVE ELEMENT WHICH INCLUDES A PHOTOCONDUCTIVE INSULATING LAYER, SAID LAYER COMPRISING THE VITREOUS ALLOY OF SELENIUM, BISMUTH AND IODINE COMPRISING ABOUT 1 TO 5 ATOMIC PERCENT BISMUTH, 2 TO 5 ATOMIC PERCENT IODINE, WITH THE BALANCE SUBSTANTIALLY SELENIUM.
 2. The element of claim 1 in which the composition comprises about 3 atomic percent bismuth, about 3 atomic percent iodine and about 94 atomic percent selenium.
 3. A photoreceptor member comprising an electrically conductive support member having a photoconductive insulating layer thereon, said photoconductive layer comprising a vitreous alloy of about 90 to 97 atomic percent selenium, 1 to 5 atomic percent of bismuth and 2 to 5 atomic percent iodine.
 4. The member of claim 3 in which the photoconductor composition comprises about 94 atomic percent selenium, 3 atomic percent bismuth and 3 atomic percent iodine.
 5. A photoreceptor member which comprises: a. a supporting member; b. a thin layer of a vitreous selenium-bismuth-iodine photoconductive alloy overlaying said support; and c. a layer of an electrically active organic material overlaying said photoconductive layer.
 6. The member of claim 5 in which the photoconductive layer is about 0.03 to 1.0 microns in thickness.
 7. The member of claim 6 in which the active layer is about 10 to 20 microns in thickness.
 8. The member of claim 5 in which the active material comprises a material selected from the group consisting of polyvinyl carbazole and polyvinyl pyrene.
 9. A method of imaging comprising: a. providing a xerographic member which includes a photoconductive insulating layer having a composition comprising a vitreous alloy of selenium, bismuth and iodine in a concentration of about 1 to 5 atomic percent bismuth, 2 to 5 atomic percent iodine, with the balance substantially selenium; b. substantially uniformly electrostatically charging said member; and c. exposing said member to a pattern of active radiation to form a latent electrostatic image thereon.
 10. The method of claim 9 which further includes developing said image to make it visible. 